In recent years, an optical scanning endoscope, which scans an observation portion optically in a spiral form by light guided through an optical fiber and receives the light reflected on the observation portion to form an image, is suggested (e.g., U.S. Pat. No. 6,294,775 and Japanese Patent Provisional Publication No. 2010-162089). The optical scanning endoscope is equipped with a single-mode optical fiber in an endoscope therein, which is held in a state of a cantilever by a piezoelectric actuator arranged in the vicinity of a tip end of the optical fiber. The piezoelectric actuator vibrates (resonates) the tip end of the optical fiber two-dimensionally in accordance with a characteristic frequency while modulating and amplifying the amplitude of the vibration so that the tip end of the optical fiber is driven in the spiral form. As a result, illumination light guided from a light source through the optical fiber is emitted to scan on the observation portion in the spiral form, and an image corresponding to an illuminated range (a scanning area) is obtained.